In such pressure caps for openings in tanks, in particular in automobile radiators, which are known from published international application, WO 95/32904, the movement of the coupling insert between the handling element and the locking element of the outer cap component is controlled by the temperature via a memory spring. In such cases, the memory spring lies inside the inner cap component on the side of the valve assembly that faces away from the inside of the tank. It was found that this remote arrangement of the memory spring causes problems and delays in measuring the temperature prevailing inside the tank, which leads to less than satisfactory results in activating and deactivating the anti-rotation means.